There are precious few legislative days left for Congress to approve the supplemental 2017 budget and keep the government funded through the rest of the fiscal year, but negotiations hit a snag over Democratic and Republican skepticism over President Donald Trump's request for approximately $1 billion to fund start construction of the controversial southwest border wall.

Two months ago, as negotiations got underway for the spending bill, Democrats made their opposition to the wall crystal clear, saying they would risk a government shutdown rather than appropriate money for something Trump previously promised would be paid for by the Mexican government.

In recent days and weeks, Republicans in the House and Senate have found themselves on the same side as those Democrats, and are encouraging Trump to hold off his push for wall funding until the White House and Department of Homeland Security (DHS) can present a full plan and fully explain how the money will be spent.

So far, the White House has been unwavering in its demand. On Monday morning, Trump took to Twitter to defend his border wall, portraying it as the only way to stem the flow of illegal drugs and dangerous gangs across the border. He also defended his request for U.S. taxpayer dollars saying that "eventually ... Mexico will be paying, in some form, for the badly needed border wall."

It remains to be seen, however, whether Trump and Congress will go all the way to risk a government shutdown over wall funding. Asked on Fox News Sunday whether Trump would veto a spending bill that did not fund the wall, White House budget director Mick Mulvaney said simply, "We don't know yet."

Even with the April 28 budget deadline looming, Mulvaney emphasized that "the negotiations are not finished yet" adding that "I don't think anybody foresees or expects or wants a shutdown."

According to Senate Minority leader Chuck Schumer (D-N.Y), the White House needs to step away from the congressional talks and stop pressuring members of their own party on the issue of the border wall.

"The four parties were negotiating quite well ... until Donald Trump and the White House threw a monkey wrench into this with the wall," Schumer said in a Monday morning press call. Republicans, he continued, should convince Trump to hold off on the funding push until some distant point in the future.

"Instead of risking government shutdown by shoving this wall down Congress' and the American people's throats, the president ought to just let us come to an agreement. And we're happy to debate this wall in regular order down the road, once he has a plan," Schumer argued.

If Democrats and Republicans are unable to reach an agreement by Friday to fund the government or pass a continuing resolution, one of the two parties is going to be blamed for a disastrous and disruptive government shutdown. Traditionally, Republicans have received the brunt of blame for recent government shutdowns, as their party has held the majority in both houses of Congress.

The American people have no desire to see the government shut down over border wall funding. In a recent Economist Group/YouGov poll, 60 percent of Americans said it was more important to keep the government running than get funds for the wall. A mere 19 percent believed Congress should provide the funding, regardless of the consequences.

Attorney General Jeff Sessions argued on Monday morning that regardless of past precedent, a government shutdown would fall squarely in the lap of the Democratic Party. "Whenever the government is shut down people blame the Republicans, but let me tell you it will be the Democrats that shut this government down to block the funding of the wall," the attorney general stated.

The White House is planning to send a bill to Capitol Hill with money for the wall, Sessions said, insisting that Congress can find "a host of ways" to pay for the wall, including passing costs on to Mexico in the form of fees.

Even as the White House begins to talk about cost, it is unclear to legislators just how large the bill will be. According to aDHS report, the total cost for constructing the wall will be $21 billion and could take three years to complete. The DHS estimate is far greater than what Trump promised on the campaign trail, a border wall costing between $10 to $15 billion, but far less than the recent cost estimate produced by Democratic staff on the Senate Homeland Security Committee.

According to the Democrat's estimates, the proposed 30 foot-high concrete wall along the southern border could end up costing U.S. taxpayers $70 billion, not including legal fees and the cost of land acquisition.

A lawsuit has already been filed against the Trump administration by the Center for Biological Diversity, a prominent environmentalist group, and progressive congressman Raul Grijalva (D-Ariz.) on the grounds that the structure would violate laws protecting endangered species and public lands.

As for the costs of land acquisition, there are many farmers and ranchers with private property along the border with Mexico who are prepared to oppose any federal government claims to eminent domain.

The cost of the wall is also a big concern for conservative budget hawks. Texas congressman and chairman of the House Homeland Security Committee, Rep. Mike McCaul said back in March that his committee would "like to see what the plan is before we write a big check." A committee aide who works with Rep. McCaul said on Monday that the chairman "continues to assess and review all funding options" when it comes to building a barrier to secure the southwest border.

Over the weekend, Rep. Peter King (D-N.Y.), a top lawmaker on the Homeland Security Committee, signaled that the administration should wait until later this year to get funds for the wall, rather than pushing it through the 2017 bill. "There’s going to be compromises going on," King said on Fox News. "Once the government is up and running, and stays open and running, then we have to fight this out over the next year."

Other border-state skeptics include Arizona congresswoman Martha McSally and her Republican colleague from Texas, Rep. Will Hurd who sent a letter to DHS in March requesting additional details about the wall. The two wanted further explanation about the nearly $1 billion funding request that they said "deserves additional scrutiny to ensure funds are being used effectively." The congressmen have been in touch with the White House regularly on the request, but are awaiting an official written response.

On both sides of the aisle, lawmakers say they want stronger border security, but want to ensure that less costly options like surveillance technology, drones, and additional personnel at the border are not overlooked in the name of keeping a campaign promise.

The White House push to begin immediate construction on the barrier is also running into some resistance from Texans, with 60 percent opposing the construction of the wall in an April poll by the Texas Lyceum.

According to David Ray, communications director at the Federation for American Immigration Reform (FAIR), even the highest estimates for the up-front cost of the wall pale in comparison to what state and local governments pay to subsidize illegal immigration.

"Hopefully Congress is going to be able to come up with the money and the political will to fund Trump's border wall, because one way or the other they're going to pay for it," Ray said, noting that FAIR estimates the annual cost of illegal immigration is upwards of $100 billion. "The option of doing nothing is extremely expensive," he warned.

The political costs for President Trump could be be high if he fails to make good on one of his most famous campaign pledges and one that many people believe was indispensable to his victory in November.

Ahead of Trump's 100th day in office, Democrats are waging a campaign to highlight "100 days of broken promises," and taking aim at his most popular pledge to build a wall and get Mexico to pay for it.

California Democrat Rep. Adam Schiff called accused Trump of breaking his promise to have Mexico pay for the wall over Twitter on Sunday, saying that "Taxpayers will bear the brunt" of the cost, not Mexico.

Ray explained that while the American public should not expect Mexico to send a check to the Treasury, there are "many alternatives" for eventually recovering the money from Mexico.

FAIR has calculated that the U.S. government could recover $460 million annually by imposing a two-dollar border crossing fee for pedestrians, passengers and vehicles. That stream of income, he said, "would eventually pay for the entire border wall." Attorney General Sessions has proposed similar fee structures.

Both the Senate and the House will be back in session on Tuesday after a two-week long recess. That means members of Congress and the White House will have only three days to reach an agreement on the levels of funding for border security, and whether that funding will include money for the southwest border wall.